What effect does the Jazz switch have on an ODS?

[bluesfendermanblues]

Ok here we go:
First : The tonestack. The Treble pot should be 500KL, you can see in the pictures that it is much larger than the CTS pots. The cap is a 510 pF ,at least it is in my amp.The Middle pot is a 250 KA (10 % taper).The caps wired to the Bass pot should be .002 (top to wiper) and .022 (wiper to
10 K resistor.)The Bass pot is a 1 Meg Audio (30% taper).You can see that this is a completely different tone stack.The grid stopper at V 1a is 56K.
I have to speculate about the input section of the Overdrive: I have seen at least three amps with this: First, a 220 K resistor to ground with 500 pF cap across it, then a 1.2 Meg resistor followed by 33 K to ground, then another 56 K grid stopper.A tech who has serviced a number of these amps (# 19 - #45 ) told me most of these amps were very similar.
There´s one thing you can see for yourself in the pictures: The 180K resistor to ground after V2b is connected directly to the .01 coupling cap, so it does not form a voltage divider with the large resistor in series with the cap, as shown in the schematic.I don´t know the value for the big resistor, it has been changed in my amp at some time.
The PI input coupling cap is .005, you can roughly estimate the value of the orange drops by their size in the pictures.
The cap on the Accent switch should be a 1 µF electrolytic, the 100n in the schematic would have very little effect across the 100 R resistor in the feedback circuit.2.2 µF is also possible here.
I hope I haven´t forgotten anything.Well,yes, the grid stoppers on V2a and V2b should also be 56 K.
The amp I mentioned in an ealier post (once belonging to a friend of mine) was very similar, except it had a 250KL Treble pot, and the .022
cap on the Bass pot was missing, making it much bassier sounding.
Hope all this information makes things a little clearer

Marcos, thats just a great example of sharing info. Thanks for the detaileds. Perhaps IC-Racer will update the earlier shoot at the #40 schem??

How about the sound of your amp? is it grail tone a la the David lindley "running on empty" solo, which would make it a must have in my book.

[two tone]

thank you Marcos,that´s great info.
Could you tell us about the cathode caps,
what value for the Overdrive pot?
Regards Hanno

[marcos]

OK guys here´s more: The cathode caps are 4,7 µF for all stages, in this case Illinois caps, not Sprague.I had them out of the amp at one time, one cap measured 2,7 µF.The Overdrive Level pot is 100 KL, just the usual stuff.Like many people I wasn´t 100% percent happy with the tone in original condition, the Overdrive was a bit raw and fuzzy, so over the years the amp has been modified a bit, actually with some help from HAD (thanks again !).Without going into every little detail, IMHO the biggest weakness of this and similar amps is the voltage divider in the OD input, it basically kills most of the gain of the following stage, making this essentially a single stage overdrive.The usual solution of the 220K/100 K trim pot combination here remedies this, in my amp I have a fixed voltage divider(220 K, 33K to ground).Overall, I think the suggestions on this forum on how to tweak a silverface ODS are excellent, and in my experiments I have come to the same conclusions, some final adjustments are always a matter of taste.
When I did recordings with this amp in the early eighties (with the amp still in almost original condition) I got a tone not quite unlike David Lindley´s, although I suspect the very early amps differ in a number of ways.However, if you listen to the recordings of Lindley, Lowell George,
Rick Vito etc, I think some of the rawness is detectable.So my guess is that none of these amps had snubbers, and all of them were low plate versions.Just a guess though

[two tone]

Marcos,what speaker are you using?
Seems to me when playing through
an original Altec or JBL, the Accent switch
is completely useless(much too bright).
Good though with an EVM or Celestion 65

[marcos]

I´m currently using Tone Tubbies, although my amp originally came with
an Altec, and yes, I thought the Accent switch was a bit too much in this combination.That was the reason I had the amp modified with a presence control, after seeing photographs of Rick Vito´s amp, again with Mr. Dumble´s help.Definetely an improvement, but I agree that with certain amp/speaker combinations the accent switch really made sense.

[Structo]

Thanks for the info Marcos.

Do you still keep in contact with HAD?

I often wonder if he has ever visited here.

[marcos]

No, I haven´t dealt with HAD in a long time, all I can say that he was very helpful every time I needed advice.I would guess that he is loooking at thhese pages sometimes

[ic-racer]

Marcos, thats just a great example of sharing info. Thanks for the detaileds. Perhaps IC-Racer will update the earlier shoot at the #40 schem??

How about the sound of your amp? is it grail tone a la the David lindley "running on empty" solo, which would make it a must have in my book.

I just saw this thread. My 70s project is on the back-burner, but I did make all the boards and start filling them with components.

I can update the schematic based on this info from marcos.

[bluesfendermanblues]

Marcos, thats just a great example of sharing info. Thanks for the detaileds. Perhaps IC-Racer will update the earlier shoot at the #40 schem??

How about the sound of your amp? is it grail tone a la the David lindley "running on empty" solo, which would make it a must have in my book.

I just saw this thread. My 70s project is on the back-burner, but I did make all the boards and start filling them with components.

I can update the schematic based on this info from marcos.

[Max]

all I can say that he (Alexander Dumble) was very helpful every time I needed advice.

Hi marcos,

I doubt that Alexander would feel well rewarded for his help (without charging a cent - as far as I understand your posts) if he knew of your very special way to say "Thank You!" by opening up your amp for public inspection.

Kind regards

Max

[Structo]

When did he show us the insides of his amp?

You seem to act like you are a personal friend of HAD.

If so, your very presence here would contradict that.

[marcos]

To put things in perspective: I was answering the questions to keep people from wasting their time by building an amp off of a schematic with a number of mistakes.I´m sure the professional builders all know the details anyway, so there´s no big secret here. The early amps weren´t gooped, plus there´s not that much demand for these amps.I doubt that we´ll be seeing a Ceriatone "Santa Cruz Model" .The ethical aspects of this forum have been discussed at length here, so I will not comment on this any further.However, I remember Max was asking similar questions in some of his posts.